The present invention relates to a method for evaluating color picture tubes and device for the same and method for making color picture tubes. The present invention seeks to provide quantitative evaluations of focus characteristics of picture tubes having color selection mechanisms.
Focus characteristics of a picture tube are an important factor that affects display image quality.
In the past, various devices have been proposed to automatically measure focus characteristics by measuring electron beam intensity distributions.
Color picture tubes include color selection mechanisms such as shadow masks and aperture grills. Since the greater part of the electron beam is blocked by these, a method in which an electron beam casts a spotlight on a particular position of the picture tube display and an imaging element is used to capture an image of this spot will not provide an adequate amount of data (luminance information for multiple positions within the beam cross-section) for determining the shape of the electron beam.
To overcome this, Japanese laid-open patent publication number Hei 8-203436 discloses a device for measuring the shape of an electron beam. An electron beam is beamed to multiple fluophors with the beam being aimed with slight horizontal and vertical variations. The multiple fluophors are imaged for each beam position. The relative light emission positions and luminances of the multiple fluophors within the electron beam for each of these beam positions is used to calculate the electron beam shape. However, measurements using this method are time-consuming.
To overcome this problem, Japanese laid-open patent publication number 10308955 discloses a device for measuring the shape of an electron beam. In this device, a measurement pattern, formed from multiple identically shaped basic patterns arranged in a row, is displayed on the display surface of a color picture tube. The size display is controlled so that each basic pattern is positioned differently relative to the fluophors. This is then imaged, and the resulting image data is used to determine relative positions and luminances of fluophors in the basic patterns. From this, the electron beam shape is calculated.
However, this device requires display size to be adjusted so that the basic patterns can be displayed with different fluophor positions. This is time-consuming and also distorts the electron beam. Also, display distortions on the picture tube can prevent different relative positioning of fluophors even with display size changes.
Also, brightness components of 1% or less need to be measured since the eye can easily perceive 1% or less of maximum luminance in an area with lit fluophors.
However, with the device above, sensitivity could only be to 5% brightness due to imaging noise and quantization errors.